In findings published last week in the Proceedings of the National Academy of Sciences (PNAS), researchers from New York University School of Medicine found that electronic cigarette smoke (ECS) can cause DNA damage in mice, which can inhibit DNA repair in the lungs and bladders, potentially signaling a risk of lung cancer and bladder urothelial hyperplasia.

Researchers exposed mice to nicotine vapors from electronic cigarettes for 54 weeks. The same researchers previously tested mice for exposure for 12 weeks, finding it appeared to cause DNA damage.

According to the findings, 22.5% of mice exposed to vaping developed lung adenocarcinomas and 57.5% developing bladder urothelial hyperplasia.

“These lesions were extremely rare in mice exposed to vehicle control or filtered air. Current observations that ECS induces lung adenocarcinomas and bladder urothelial hyperplasia, combined with our previous findings that ECS induces DNA damage in the lungs and bladder and inhibits DNA repair in lung tissues, implicate ECS as a lung and potential bladder carcinogen in mice,” the researchers concluded. “While it is well established that tobacco smoke poses a huge threat to human health, whether ECS poses any threat to humans is not yet known and warrants careful investigation.”

The findings were published just days after the U.S. Centers for Disease Control and Prevention issued an update on the e-cigarette illness outbreak, which indicates that vaping may be responsible for more than 1,000 illnesses and about 20 deaths nationwide.

Amid growing concerns about these potential vaping side effects, there has also been increased scrutiny of e-cigarettes by U.S. regulators and health officials, especially involving the widespread marketing of JUUL and other devices that has been directed towards teens and prior non-smokers.

As a result of high levels of nicotine contained in e-cigarettes, there is now an epidemic of vaping and teens addicted to JUUL in the United States, leading to bans on certain flavored products designed to appeal to minor.

A number of JUUL addiction lawsuits are also now being pursued against the manufacturers, alleging that the products were illegally marketed to kids while failing to disclose that each of the e-cigarette pods contain more nicotine than a pack of tobacco cigarettes.